The application of aqueous conveyor lubricants for lubricating and possibly also cleaning and disinfecting conveyor systems, specifically for lubricating the interface between a container and a moving conveyor belt or track surface, is well known in prior art. If a conveyor system is not lubricated sufficiently, this can lead to the falling down of the containers or have the result that the containers do not stop, even though they have reached a filling, cleaning or labelling station. Both kinds of malfunctions can lead to longer standing times of the conveyor system and to a considerable loss of capacity.
Aqueous conveyor lubricants are usually applied in very low concentrations e.g. in a range from 0.1% to 2%, while the necessary quantity of aqueous conveyor lubricant is high. The exact determination of concentration of the applied lubricants is of a high significance, in order to guarantee an optimal lubrication of the conveyor system.
Presently the concentration of aqueous conveyor lubricants is determined by manually retaining a sample of the conveyor lubricant and examining it by titration. This method is very inaccurate, due to the difficult recognition of the equilibrium point during the titration. Furthermore, this analysis technique takes a long time to obtain results and is not adapted for an on-line application.
The present invention seeks to avoid these disadvantages by proposing a technique of measuring by a spectro-photometric method, particularly by the absorbance of light, which is simpler, faster and easier to implement than the laboratory method discussed above. Furthermore, this method can be adapted to use on-line.
Many molecules absorb ultraviolet or visible light. Lambert-Beer's Law is a mathematical means of expressing how light is absorbed by matter. The Law states that the amount of light emerging from a sample is diminished by three physical phenomena:                1. The amount of absorbing material in its path length (concentration)        2. The distance the light must travel through the sample (optical path length)        3. The probability that the photon of that particular wavelength will be absorbed by the material (absorptivity or extinction coefficient). This relationship may be expressed as:A=ebc        
were
A=absorbance
e=molar extinction coefficient
b=path length in cm and
c=molar concentration.
Different molecules absorb radiation of different wavelength. An absorption spectrum will show a number of absorption bands corresponding to structural groups within a molecule. An absorption spectrum shows the absorption of light as a function of a wavelength.
The determination of a concentration by measuring the absorption of light is a modern, reliable and competitive method, which is applied especially for industrial waste-water analysis.
Examples for the concentration detection of a component of an industrial water system can be found in U.S. Pat. No. 5,419,837 or in US 2004/013221 A. U.S. Pat. No. 4,666,858 teaches the determination of the quantity of anionic material in electrolyte metal plating baths by spectro-photometrical measuring the ultraviolet absorption of the extracted material.
DE-A1 42 34 466 is directed to a method for the determination of the concentration of a substance within a solution. This document teaches the use of a tracer, which is a fluorescence dye, the concentration of which is measured by an optical method.
An object of the present invention is to provide a method of lubricating a conveyor system, which assures an optimal concentration of the applied lubricant.
Another object of the present invention is to make a conveyor system more efficient by avoiding standing times and increasing its transport capacity. Another object of the present invention is to permit the on-line determination of the concentration of an aqueous conveyor lubricant, which is applied to a conveyor system.